Field of Invention
The present invention relates to a flyback power converter, and a controller and a driver thereof; particularly, it relates to such a flyback power converter which generates an ON pulse signal and an OFF pulse signal at a secondary side of a transformer therein, which are transmitted to a primary side of the transformer to determine a start conduction time point and an end conduction time point of a primary winding, and a controller and a driver of the flyback power converter.
Description of Related Art
FIG. 1 shows a schematic diagram of a conventional flyback power converter 100. As shown in FIG. 1, a rectifier circuit 101 rectifies an alternating current (AC) voltage Vac to generate an input voltage Vin. The rectifier circuit 101 is for example a bridge rectifier circuit. A primary winding W1 of a transformer 102 of the flyback power converter 100 receives the input voltage Vin. A power switch SW controls a conduction time of the primary winding W1, and the input voltage Vin is converted to an output voltage Vout which is generated at a secondary winding W2 of the transformer 102. The flyback power converter 100 includes the aforementioned transformer 102, the power switch SW, an opto-coupler circuit 104, a pulse width modulation (PWM) controller 105, a current sense circuit 106, a synchronous rectification (SR) control circuit 107, and an SR switch circuit 108. The power switch SW is controlled by a switching signal GATE which is generated by a feedback control loop. More specifically, the PWM controller 105 generates a PWM signal according to a feedback signal COMP related to the output voltage Vout and a current sense signal CS related to a current flowing through the power switch SW. The feedback signal COMP is for example generated by the opto-coupler circuit 104 (or, alternatively, generated by an auxiliary winding which is not shown). The current sense signal CS is generated by the current sense circuit 106. The PWM signal is for generating the switching signal GATE, to control the power switch SW for converting the input voltage Vin to the output voltage Vout.
Still referring to FIG. 1, for better power conversion efficiency, the secondary winding W2 of the flyback power converter 100 is electrically connected to the SR switch circuit 108. The SR control circuit 107 controls the SR switch circuit 108 according to a voltage drop across the SR switch circuit 108. As such, the secondary winding W2 is controlled to be conductive while the primary winding W1 is not conductive, for converting the input voltage Vin to the output voltage Vout. However, if the secondary winding W2 is conductive while the primary winding W1 is still conductive, a “short through” occurs. In certain cases, for example when the flyback power converter 100 operates in a continuous conduction mode (CCM), it is possible that the SR switch circuit 108 is not timely turned OFF while the primary winding W1 is still conductive, such that the aforementioned short through occurs to damage the flyback power converter 100.
In view of the above, the present invention proposes a flyback power converter, and a controller and a driver thereof, wherein the flyback power converter generates an ON pulse signal and an OFF pulse signal at a secondary side of a transformer therein, which are transmitted to a primary side of the transformer to determine a start conduction time point and an end conduction time point of a primary winding, so as to avoid the short through problem.